1. Field of the Invention
The invention relates to gas turbine engine turbine disk and blade cooling and in particular to inducers used to tangentially inject cooling air from a static section of the engine to a section of the engine's rotor.
2. Description of Related Art
Gas turbine engine's efficiency and specific fuel consumption are greatly improved by employing higher temperature turbine flows. In order to operate at higher turbine temperatures, turbine rotors and their blades are designed to use cooling air gathered and transferred from static portions of the engine. In order to efficiently transfer the cooling air, tangential flow inducers have been designed, usually in the form of a circumferentially disposed array of nozzles to accelerate and turn the cooling flow so as to tangentially inject the cooling flow into rotating rotors at a rotational or tangential speed and direction substantially equal to that of the rotor.
An example of such an inducer may be found in U.S. Pat. No. 4,882,902 to James R. Reigel et al., entitled "Turbine Cooling Air Transferring Apparatus", assigned to the same assignee, and incorporated herein by reference. Reigel incorporates circumferentially curved radially extending vanes forming nozzle type cooling air flow passages therebetween to accelerate and turn the cooling flow. Inducer nozzles having circular cross-sections are shown in U.S. Pat. No. 4,425,079 to Trevor H. Speak et al., entitled "Air Sealing for Turbomachines", and in U.S. Pat. No. 3,980,411 to David Edward Crow, entitled "Aerodynamic Seal for a Rotary Machine".
The inducers in the prior art all inject the cooling air flow in a direction that is tangent to the operational direction of rotation of the rotor. The velocity vector of the flow also has an axial component that causes flow losses at the transfer point, particularly along the edge of the exit hole.
The velocity distribution of the accelerated flow produces a substantially jet like flow from each of the inducer nozzles, creating an annular, series of these jets. Cooling flow separation may occur between the jets which result in high flow losses and lowers the operating efficiency of the engine.
The separated air flow problem of prior art inducers is particularly acute for inducers having small radially extending inducer heights, as measured from the engine centerline. Such designs are very useful in engines having low cooling air mass flow rates through the inducers. Cylindrical cooling air flow holes or passages provide a very aerodynamically efficient means for tangential injection of the cooling air into the rotor; however, cylindrical air flow passages, because of their well formed and discrete jets, produce separated flow regions between the cooling air injection jets which is undesirable as explained above.